Blast furnace process



April 1942- c. a. HOGBERG ETAL 9,399

BLAST FURNACE PROCESS Filed 001;. 4, 1939 aw M 5 Rm 0 m e C m Patented14, 1942 anus-r FURNACE rnocEss Carl G, Hogberg and George E. Steudel,

Application October 4, 19 9, Serial No. 297,94 2 Claims. -(CI. 75-41)invention relates to metallurgy, and more particularly to 'themanufacture of pig iron in a blast furnace, and one of the objects ofthe-present invention is to provide an improved blast furnace process.Another object is to introduce required flux materials within the blastfurnace at the point the said materials are needed. Still another objectis to increase the operating efiiciency of a blast furnace. Otherobjects and advantages will be apparent as the invention is more fullyhereinafter described.

In accordance with the above objects we have discovered that the greaterportion of the fluxing material, limestone or similar calcareousmaterial, which is added to the usual burden fed to. the blast furnacein admixture with the oreand coke, serves no useful purpose and is infact deleterious to the desired ore reduction, until the said fluxmaterial reaches the lowest heat zone in the furnace, and that the samemay be most advantageously omitted'in major part from the burden mixtureand fed instead to the furnace at the said lowest heat zone, with markedadvantage on the furnace efllciency and on the furnace capacity, as wellas more effectiveLv performing its intended function of de-sulfurizingthe pig iron product produced in the furnace.

In the operation of the blast furnace process, the materials within thefurnace undergo a series of transitions between the molten, solid, andgaseous states. These transitions are generally confined to variouszones.- In order to more clearly describe these zones within the blastfurnace. reference will be made to the attached drawing wherein isillustrated in vertical cross-section a typical blast furnace, togetherwith the improved means of the present invention, the latter being shownpartly. in elevation and partly in fra mentary section.

'In generalgthe usual blast furnace process is a countercurrent reactionof descending solid and' molten material with that of ascending gases.

The solid constituents of the blast furnace charge consist of fuel(carbon), iron-bearing material (ore), and fluxing material (limestone).These are dropped into the top T of the furnace F in more or lessadmixture wherefrom they descend" is heated sufliciently to drive oifthecarbon dioxide from the calcium carbonate of the limestone. Thecarbon dioxide gas thus liberated unites with the ascending gas mixtureand passes through the stock column-and out of the furnace. In region Xthe constituents of the charge are predominantly in a solid state. Inregion B, however, the solid constituents of the charge become molten asthey pass downward through the hotter zone and drop into the furnacehearth, where the slag layer S forms above the iron layer I.

Region B is an important one for it is here where the gangue materialsof the charge melt and unite to form slag. The ease of penetration anduniform distribution of gases passing through this region, the contactof the gases with the unreduced iron-oxides, and the rate of movement ormaterial through the furnace, are greatly dependent upon the amount andphysical characteristics of the slag formed.

The production of slag, although it be incidental to the production ofmetal, is important in that it sets alimit upon the chemical and thermalrequirements of the process as a whole. The slag is formed by fusion ofcertain impurities in the materials charged into the fur-'- nace. Inpractically all cases, the chemical balance of impurities in thechargedfuel and metalbearing materials is such that the fusion of thoseimpurities alone results in the formation of a slag whose properties areconducive neither tosmooth and economic furnace operation nor toadequate desulfurization of the metal product. As a result, it isnecessary to charge additional limestone material, known as flux, insuch proportion asto form a slag whose properties will permit smoothfurnace operation and chemically inhibit the inclusion of certainundesirable constituents in the metal product.

The common means of obtaining a properly fluxed slag is to charge theflu'xing material, usually in the form of limestone or a similarcalcareous material, into the top of the furnace in admixture with thecarbon and ore wherefrom it descends into the hotter zones of thefurnace andin the descent is first calcined to calciumoxe d' n sm l fi-A; large proportion of the flux added at the p. of ihs ilrn q ildfid.geld: e i purwith the molten'oxides contained in the ironbearing andfuel materials. This condition does not exist excepting in the slag bathwhich is located below the tuyeres and in one of the lowest zones of thefurnace. Indeed, the presence of this added flux material in furnacezones above that of the molten slag surface is essentially detrimentalto the smooth and economic operation of the furnace for the followingreasons:

1. The presence, in zones where it is not necessary to the successfuloperation of the process, of a large portion of calcareous fiuxingmaterial, either in a molten or solid state, is detrimental to theprocess in that it (a) impairs the contact of the unreducedmetal-bearing materials with that of the gases, thus delaying thereduction of that material and (b) decreases the reducing power of thefurnace gases as a result of a liberation from the flux of inert carbondioxide gas which-dilutes the gas mixture and makes less effective thestrong reducing power of carbon monoxide.

2. The presenceof a high lime (CaO)' content flux in the 'higher fusionzones of the furnace results inthe production, in those zones, of a slagwhose melting temperature is considerably in excess to that of a slagformed from the fusion of "the impurities of the charge other than thosintroduced by the fiuxing material.

. 3. The smooth and economic operation of the furnace is'impaired by thehigher viscosity. inherent with the higher lime content molten mixturesas exist before the fusion of the oxides material is charged at B. Thefiux material flows by gravity down .the inclined bottom walls of thecontainer A through outlet opening into an aspirating chamber G.Preheafed air obtained from a hot blast main by a pipe D is passed firstthrough a compressorE which forces the air blast through the aspiratorQ. The fiuxing material falling through openlngO is carried by thestream of the air blast into one or more pipes P leading to the interiorof the furnace F at a point (or points) below the normal fusion tzone13.

Thus introduced, the preheated calcium oxide (calcined limestone) infinely divided form readily fuses and reacts with the impurities in themelting and melted charge to form a fluid slag overlying the moltenmetal Ion the hearth of the furnace F. The oxygen content of thepreheated gases from the hot blast main, augment the usual air blastsupplied by tuyeres W and increase the sensible heat energy beingsupplied to the furnace F. v

Having hereinabove disclosed the present invention generically and givenone specific embodiment of the same, it is believed apparent that thesame may be widely varied without essential departure therefrom and allsuch modifications of that slag with the more siliceous and alumiv nousoxides of the coke ash.

4. Experience has proved that the rate of iron production decreases whenthe slag formed is excessively limy, that is, excessively high incalcium oxide;

For reasons outlined above, the present invention proposes to add eitherpart or=all of the flux to the materials within the furnace in-a mannerand at a point in the furnace that will result in the elimination, to agreat degree, of the disadvantageous conditions as outlined above.

We propose to accomplish this result by adding .a calcined preheatedfluxing material to the aggregate within the furnace F at a point belowthe normal fusion zone of the furnace by means of the apparatusillustrated in the drawing. We have determined that by adding thepreheated calcium oxide to the charge in the furnace at a point below}the normal fusion zone of the fur-'- nace the disadvantageous aspectsassociated with the higher lime content slags in the slag fusion zone ofthe furnace (zone B) may be eliminated withbuhideleteriously affectingthe elimination of sulfur in the blast furnace process, while at thesame time increasing the reduction efliciency of the process and. thecapacity of the furnace.

Theapparatus used to practice the process of the invention comprises aninsulated container A into which a powdered preheated calcined flux andadaptations of the same are contemplated as may fall within the scope ofthe accompanying, claims.

What we claim is: i 1. The method of reducing iron ores in a blastfurnace whichincludes charging into the upper part of the furnace ironore admixed with carbon, preheating finely divided calcinated limestone,blowing by preheated air the preheated finelydivided calcinatedlimestone into the lower part of the furnace at a point below the normalfusion zone thereof but above the zone of molten material on the furnacehearth, regulating the introduction of the preheated air and thepreheated finely divided calcinated limestone to produce stratificationof the limestone in a layer immediately adjacent to and overlying thesurface of the molten metal bath within the furnace hearth, andcontinuing the introduction of the preheated air blast and the preheatedfinely divided calcinated limestone until there has been introduced tothe blast furnace a quantity of limestone approximately equivalenttothat required by the ash in the carbon burned.

2. The method of reducing iron ores in a blast furnace which includescharging into the upper part of the furnace iron ore admixed withcarbon, preheating finely divided calcinated calcareous fiuxing agent,blowing by preheated air the preheated finely divided calcinatedcalcareous fluxing agent into the lower part of the furnace at a pointbelow the normal fusion zone thereof but above the zone of moltenmaterial on the furnace hearth, regulating the introduction of thepreheated air and the preheated finely divided calcinated calcareousiluxing agent to produce stratification of the said fiuxing agent in alayer immediately adjacent to and overlying the surface of the moltenmetal bath within the furnace hearth, and continuing the introduction ofthe the carbon burned. g CARL G. HOGBERG.

GEO. E. STEUDEL.

